Vinyl acetate is commonly produced by the reaction of ethylene, oxygen and acetic acid in the presence of a palladium-gold catalyst. See, for example, U.S. Pat. No. 3,743,607. Palladium and gold are expensive precious metals. Therefore, many efforts have been made to increase the catalytic activity and reduce the amount of catalyst needed. For example, U.S. Pat. No. 6,022,823 teaches calcining the support impregnated with palladium and gold salts prior to reducing the metals. The catalyst shows improved activity. These prior patents are herein incorporated by reference in their entirety.
The acetoxylation of ethylene to vinyl acetate is commonly performed in a gas phase, fixed bed tubular reactor. Vinyl acetate is recovered by condensation and scrubbing, and purified by distillation. Unreacted ethylene, oxygen and acetic acid are recovered by distillation and recycled to the acetoxylation.
In addition to vinyl acetate, the acetoxylation produces a number of byproducts, including carbon dioxide, water, ethyl acetate and ethylene glycol diacetate. Carbon dioxide is primarily produced by the combustion of ethylene and vinyl acetate. Carbon dioxide is removed from the reaction product mixture by distillation and absorption with a potassium carbonate solution.
Copending U.S. patent application Ser. Nos. 12/587,580, filed on Oct. 9, 2009, and 12/653,144 filed on Mar. 8, 2010 disclose a process for the production of vinyl acetate. The processes comprise reacting ethylene, acetic acid, and oxygen in the presence of a catalyst to produce a reaction mixture comprising vinyl acetate, ethylene, carbon dioxide, acetic acid, water and ethylene glycol diacetate. The reaction mixture is separated to a gas stream comprising ethylene, oxygen, and carbon dioxide and a crude vinyl acetate stream comprising vinyl acetate, acetic acid and ethylene glycol diacetate. An ethylene glycol diacetate stream is isolated from the crude vinyl acetate stream and hydrolyzed prior to or in the waste acid stripper column of an acetic acid plant, to recover the acetate content of the stream as acetic acid.
However, the hydrolysis pathway provides a number of logistical complexities that can be improved. These include maintaining a proper flow rate to a waste acid stripper, energy intensive separation of acetic acid from water, and a less than desirable equilibrium yield.
Accordingly, a new method for recovering acetic value from the vinyl acetate production is needed.